GB/T 16927.4 is the fourth part of the Chinese high-voltage test technique series and extends the subject to test currents and the systems used to measure them. Many dielectric tests are defined by the current that flows rather than by the voltage applied: a surge arrester is characterised by the impulse current it can discharge, a circuit breaker is tested at its rated short-circuit current, and a capacitor must withstand a discharge current of a specified waveform. The standard defines the parameters of a current waveform, including the peak value, the front time, the time to half value and the duration for the different classes of current used in testing, and it specifies the requirements for the measuring system, whether it is based on a shunt, a current transformer or a Rogowski coil. The document describes the methods by which the scale factor and the dynamic response of the system are determined, the way the record is evaluated, and the combination of the individual uncertainties into the uncertainty of the measured current.